This application claims the priority of Japanese Patent Application No. 11-189833 filed on Jul. 5, 1999, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a compact zoom lens; and, in particular, to a low-cost, compact zoom lens suitable for a lens shutter camera.
2. Description of the Prior Art
Demands for higher magnification, compactness, and lower cost have been increasing for lens systems employed in lens shutter cameras in recent years. For responding to these various demands, utilization of aspheric surfaces, use of special glass materials, arrangement of shutter position, and the like have actively been proposed.
Known as such a zoom lens are three-group zoom lenses disclosed in Japanese Unexamined Patent Publication Nos. 4-78811 and 7-20380, for example. Each of these zoom lenses comprises three groups having positive, positive, and negative refracting powers successively from the object side, and achieves a power variation ratio of about 2 to 3.5.
In recent years, however, there have been demands for further higher magnification, and further smaller size and lower cost than those of the above-mentioned prior art.
In view of such circumstances, it is an object of the present invention to provide a low-cost, compact zoom lens having a high magnification with a zoom ratio of about 4.
The present invention provides a compact zoom lens comprising, successively from an object side, a first lens group having a positive refracting power, a second lens group having a positive refracting power, and a third lens group having a negative refracting power, air spaces among the lens groups being variable so as to change a magnification;
wherein the second lens group comprises, successively from the object side, a negative meniscus lens having a concave surface directed onto the object side, a positive biconvex lens, and a positive meniscus lens having at least one aspheric surface and a concave surface directed onto the object side.
Preferably, the third lens group comprises, successively from the object side, a plastic-made meniscus lens, whose both surfaces are aspheric, having a relatively weak refracting power, and a negative meniscus lens having a concave surface directed onto the object side.
Preferably, the compact zoom lens satisfies the following conditional expressions (1) and (2):
4.5 less than fT/fG2 less than 7.0xe2x80x83xe2x80x83(1)
fG2/fG3 less than xe2x88x920.8xe2x80x83xe2x80x83(2)
where
fT is the focal length on the longer focus side;
fG2 is the focal length of the second lens group; and
fG3 is the focal length of the third lens group.
Preferably, a stop is disposed on an imaging surface side from the first lens group, and the air space between the first lens group and the stop is held constant when changing the magnification.
The present invention also provides a lens shutter camera comprising the compact zoom lens.